I have four tanks, 10g and under. I’ve been using this siphon since I started in the hobby a couple of years ago and it’s been great. Never had a problem. I have a tank with shrimp and I stretch a piece of stocking over the head so I don’t suck any up.

Luigi's Aquarium/Fish Tank Siphon... https://www.amazon.com/dp/B06XKGYJHR?ref=ppx_pop_mob_ap_share

You've got the right idea. Leopard frog tadpoles are on the larger side, so a bigger tank is definitely a good idea. Tadpole care is nearly identical to scaleless fish and basic axolotl care, so your suggestions are perfect.

You're also exactly right about how they should be cleaning the tank. Maybe you could suggest a siphon with a guard over the opening if you haven't already (like this one: https://www.amazon.com/Aquarium-Fish-Siphon-Gravel-Cleaner/dp/B06XKGYJHR/ref=mp_s_a_1_5?crid=AS62C7NEQW69&keywords=gravel+vacuum+with+guard&qid=1653312911&sprefix=gravel+vacuum+with+guard%2Caps%2C72&sr=8-5).

Aloe vera might clog their gills a bit, so I think it'd be a risk to keep using it. It might be fine, but it also might go badly.